1. Field of the Invention
In protecting metal of joints of underground pipe systems, particularly steel reinforced or prestressed concrete pressure pipe.
2. Prior Art
Several types of concrete pressure pipe joints include steel bell and spigot rings in conjunction with an O-ring to hydrostatically seal the joint. A current method for externally protecting the joint rings from corrosion is to pour portland cement grout into a recess of the joint. The method requires use of a diaper-like band to contain the grout. In addition the method requires portland cement, sand and water to be available as grout ingredients at the installation site of the pipeline. Workers mix these components to make the grout and then pour the grout into the joint recess. The grout provides an important alkaline environment to prevent corrosion of any exposed steel. Properly executed, the method effectively protects the external joint areas, but it is labor intensive and sensitive to human mistakes. In addition, hardened mortar is subject to cracking in the event that there is settlement of the pipeline. The grout band extends several inches longitudinally, on each side of the joint, in order to seal any coating cracks which may occur and which may give rise to corrosion of reinforcing steel or prestressing wire.
Prior art patents show similar arrangements but do not anticipate nor render obvious the present invention.
U.S. Pat. No. 3,228,712 to Hausmann et al. disclosed a pipe joint wherein pipe sections are joined together and grout is placed in the pipe joint which is covered by a foam and an impermeable band. The band is held onto the pipe by means of metal straps. The Hausmann invention discloses a polyethylene foam mechanically bonded to the grout in the pipe joint in order to span any cracks in the mortar occurring as a result of pipeline settlement. It is anticipated that the bands (diapers) and straps will disintegrate with time.
U.S. Pat. No. 5,527,070 to Blackwell illustrates a pipe joint wherein a plastic-like cushion layer is provided at the joint and the same is covered with a film wrap. The Blackwell invention is designed to protect relatively small diameter cast iron pipe from mechanical damage when installed in expansive soils. In addition, the entire pipe is wrapped in the plastic film.
U.S. Pat. No. 4,443,282 to Stachitas disclosed a pipe joint wherein the joint connection has an elastomeric band around the joint and mastic is provided under the band. The Stachitas band is designed to seal a non-pressure joint from infiltration of ground water.
U.S. Pat. No. 5,096,206 to Andre et al. disclosed a pipe joint sealed by mastic or a gasket and then a seal member is placed over the joint and secured by means of straps. Andre's approach discloses a band that must seal a joint which has no other means for sealing or a backup sealant when O-rings are used in the joint.
U.S. Pat. No. 5,531,485 to House et al. shows a pipe joint provided with an elastomeric band and adhesive seal arranged circumferentially around a juncture of two pipes. The House band of this invention is designed to seal a non-pressure joint from infiltration of ground water.